To stack multiple dies in a same package structure, through-substrate vias (TSVs) are used to route signals from one side of a die to the opposite side. FIG. 1 illustrates a cross-sectional view of conventional TSV 102 formed in semiconductor substrate 106. Isolation layer 104 is formed between TSV 102 and semiconductor substrate 106. It is observed that capacitor 108 is formed, with TSV 102 and semiconductor substrate 106 acting as the capacitor plates of capacitor 108, and isolation layer 104 acting as the capacitor insulator.
The TSV structure as shown in FIG. 1 suffers from drawbacks. Due to the relatively great size of TSV 102, the capacitance of capacitor 108 is high. This causes several problems. First, the noise in substrate 106 may be easily coupled into TSV 102. Second, when high-frequency signals are conducted through TSV 102, the high-frequency signals may be easily lost to semiconductor substrate 106 due to the coupling between TSV 102 and semiconductor substrate 106.